How commensal bacteria communicate with the host to modify immunity is incompletely understood. Here we propose to characterize a previously unrecognized pathway of communication between bacteria and the eukaryotic host and its role in mediating immunomodulatory effects of mucosa-associated commensals. To identify the nature of the process we will characterize the involvement and requirement of various endocytic pathways by a combination of chemical and genetic approaches. We will also generate and examine these interactions in a novel in vitro system. If successful, our studies will uncover a novel mechanism for delivery of bacterial antigens for activation of commensal-specific T cells in the intestine, and/or for delivery of bacterial molecules for immune modulation.